Neutralisation is the reaction of an acid with a base that results in the pH moving towards 7.

It is a useful process that occurs in everyday life such as in the treatment of acid indigestion and the treating of acidic soil by adding lime.

Neutralisation also moves the pH of an alkali down towards seven.

Several different bases can neutralise acids, and water is always produced as a result of these reactions.

Equations for neutralisation

Acid + alkali \to salt + water

Acid + metal\,oxide \to salt + water

Metal oxides and alkalis are two types of base. Basic substances neutralise acids, resulting in the pH of the acid increasing towards 7, and water being produced. A soluble base dissolves in water to form an alkaline solution.

Naming salts

To name the salt, the metal ion from the alkali (or base) replaces the hydrogen ion from the acid - (alkali to front, acid to back). For example:

hydrochloric\,acid + sodium\,hydroxide

\to sodium\,chloride + water

Acid nameSalt name ending
Hydrochloric acid...chloride
Sulfuric acid...sulfate
Nitric acid...nitrate

During neutralisation the H+ ion from the acid joins with the OH- ion from the alkali. This is why water is formed in these reactions.

H_{}^ +  + OH_{}^ -  \to H_2^{}O

This is true for all neutralisation reactions.

Acids can be neutralised by metal carbonates

In the neutralisation reaction between an acid and a metal carbonate, there are three products. The hydrogen ions (H+) from the acid react with the carbonate ions (CO32-) to form water and carbon dioxide gas. A salt is also produced.

Metal\,carbonate + acid \to salt + water + carbon\,dioxide

2HCl + CaCO_3^{} \to CaCl_2^{} + H_2^{}O + CO_2^{}

The salt is named in the same way as before, taking the metal's name from the carbonate and the ending from the type of acid used.

Carbon dioxide can be tested for using lime water (turns from colourless to chalky white).